Author Topic: What the? Strange Waveform? (Read 9063 times)

BayTaynt3d · « **on:** March 09, 2006, 02:30:40 AM »

Alright, maybe I'm just a newb, but I've got about 20 taping sessions under my belt at this point, and I have yet to come across this. It was my first night out with my new CK91 caps, but I'm guessing this didn't have anything to do with the caps? Most of the night looks/sounds fine, but the attached pic shows a stretch where the waveform is shifted up and clipping only on the top. WTF? Is that what phase shifting looks like? I was running XY indoors and had the caps were very much on top of each other, so I didn't think phase would be a problem. Or is this something else? At one point, I thought the caps might have been touching each other (no windscreens), but I wasn't sure. There is no obvious vibration sounds or anything like that, so I'm not sure they were touching at all. Could someone please explain what the hell happened because I'm confused? Operator error? New caps? Weird acoustics in the venue? Corrupt file?

anodyne33 · « **Reply #1 on:** March 09, 2006, 11:56:03 AM »

preamp issue. one side of the waveform +v (i'd suppose) got more voltage (or possibly less) than the other for some reason at that passage

BayTaynt3d · « **Reply #2 on:** March 09, 2006, 12:27:45 PM »

That's strange. What could cause something like that? I haven't checked the second act yet (this was the opener), but I'm hoping it's not a problem there. I ran DINA for the second act and moved my rig, so I'll check that tonight.

Roving Sign · « **Reply #3 on:** March 09, 2006, 02:07:27 PM »

Is there anything to hear? Does it sound normal in those passages...?

Sometimes - soundguys will pump up one channel while they work on some EQ issues - that can cause sudden blasts if energy- that arent necessarily noticeable live...

...but I see what your saying about it being lopsided...

BayTaynt3d · « **Reply #4 on:** March 09, 2006, 02:26:20 PM »

The lopsidedness is on both channels though. It sounded OK on first listen, but I haven't spent any quality time with it yet really -- I just opened it up last night and saw this weird section. There is some clipping in those regions as far as SF determines. But it's not like it's favoring one channel or something, this is happening in one channel's waveform.

Roving Sign · « **Reply #5 on:** March 09, 2006, 02:38:54 PM »

I meant "channel" relative to the board mix/inputs...not left or right main output...

For example - he might have bumped up the drum overhead mics - did some EQ work - and them bumped them back down...but while they were up - they might have caused some peakyness in the overall mix...

just an example...

Electric Cowgirl · « **Reply #6 on:** March 09, 2006, 02:55:06 PM »

It looks like severe overage to me. Open up the level meter and play that section. If you are slamming the zero that's all it is.

BayTaynt3d · « **Reply #7 on:** March 09, 2006, 03:16:42 PM »

I've had penty of overages before, and clipping, but the waveform is always still uniform. There's got to be more to it than that. Only ONE SIDE of the waveform is having an overage. WTF? This just doesn't seem to be a case of "levels to hot" to me. The waveform is ASYMETRICAL?

terrapinj · « **Reply #8 on:** March 09, 2006, 03:49:08 PM »

PM Sent

cleantone · « **Reply #9 on:** March 09, 2006, 03:56:07 PM »

I think it is what dot ron mentioned.

SparkE! · « **Reply #10 on:** March 09, 2006, 10:38:20 PM »

You didn't say what your recording chain is.

My first mics (homemade) made lopsided waveforms like that when run into my PCM-M1. I later replaced my coupling caps with polypropylene caps (they were originally tantalums) and that cured most of the problem. The problem was also not as bad when I ran them into a NJB3 because of the higher input impedance on the NJB3 as compared to the PCM-M1. I made a few more mods later that were designed to reduce even harmonic distortion and I don't see anything like that anymore. So, I'm betting that it's your mics or your battery box (if you use one).

BayTaynt3d · « **Reply #11 on:** March 09, 2006, 10:58:16 PM »

Chain was: CK391 > UA5 (BM2+) > JB3

It was the first night out with the 391's (I usually ran C4s). And I also think I used a spare DVD battery that I got with the FP24 I bought a few weeks back. So, I had some new things in the mix that possibly could had contributed maybe?

The good news is that the first and second sets of the main act look fine (see attachments). Not sure what happened on the opener though. Strange. I wonder if the caps ended up touched each other in my XY on the opener if that could have done it? I was running XY on stage, and although the opener wasn't miced through the PA, there was a crapload of mics and cables on stage for the main act that had 20+ artists in it, every one of whom was mic'ed. Not sure if I could have had problems with that. The main act, I pulled back to the sweet spot for the PA and went DINA, so I had a pretty different setup for the second part.

Roving Sign · « **Reply #12 on:** March 09, 2006, 11:02:49 PM »

when you first mentioned the possibility of the mics touching - I thought you were refering to mechanical noise caused by them bumping each other. But maybe - if they touched - there is some electrical contact/interaction.?

BayTaynt3d · « **Reply #13 on:** March 09, 2006, 11:10:35 PM »

There was a point, well into the set, where I looked up, and I thought they were literally touching each other for the rest of the set. By that point my levels were fine, and I was off having drinks. My stand was on stage practically, so I didn't have to guard it. When I saw it, there was nothing I could do about it because it would have been rude and distracting to try to fix it. I'm still not sure if they were actually touching or not, but maybe. Good reason to put the windscreens on though. Then even if they were touching, it wouldn't be direct contact. But still seems strange to me. I'll have to watch it over the course of the next few pulls.

CHURCH-AUDIO · « **Reply #14 on:** March 09, 2006, 11:14:24 PM »

This could be the front of house sound engineer bumping up a fader on his main system EQ. I do this from time to time to see if I have a bump in the front of house or if its comming off the stage monitor mix and when I hear something on the verge of feedback I will do it to see if its me or the monitor engineer. But still its strange its only on the + side of the wave form. Hummm maybe it could also be a sampling error?. Here is another theory What if the +- voltages on your computers PCI buss were out if you sound card is internal or even if you have a external with a voltage rail problem the opamps would have a swing towards the + or - depending on the design of the circuit.
Hey maybe its just a screwed up waveform? how does it sound?

Chris Church

Quote from: Tainted on March 09, 2006, 02:30:40 AM

Alright, maybe I'm just a newb, but I've got about 20 taping sessions under my belt at this point, and I have yet to come across this. It was my first night out with my new CK91 caps, but I'm guessing this didn't have anything to do with the caps? Most of the night looks/sounds fine, but the attached pic shows a stretch where the waveform is shifted up and clipping only on the top. WTF? Is that what phase shifting looks like? I was running XY indoors and had the caps were very much on top of each other, so I didn't think phase would be a problem. Or is this something else? At one point, I thought the caps might have been touching each other (no windscreens), but I wasn't sure. There is no obvious vibration sounds or anything like that, so I'm not sure they were touching at all. Could someone please explain what the hell happened because I'm confused? Operator error? New caps? Weird acoustics in the venue? Corrupt file?

BayTaynt3d · « **Reply #15 on:** March 09, 2006, 11:20:57 PM »

Quote from: CHURCH-AUDIO on March 09, 2006, 11:14:24 PM

This could be the front of house sound engineer bumping up a fader on his main system EQ. I do this from time to time to see if I have a bump in the front of house or if its comming off the stage monitor mix and when I hear something on the verge of feedback I will do it to see if its me or the monitor engineer. But still its strange its only on the + side of the wave form. Hummm maybe it could also be a sampling error?. Here is another theory What if the +- voltages on your computers PCI buss were out if you sound card is internal or even if you have a external with a voltage rail problem the opamps would have a swing towards the + or - depending on the design of the circuit.
Hey maybe its just a screwed up waveform? how does it sound?

Chris Church

Quote from: Tainted on March 09, 2006, 02:30:40 AM
Alright, maybe I'm just a newb, but I've got about 20 taping sessions under my belt at this point, and I have yet to come across this. It was my first night out with my new CK91 caps, but I'm guessing this didn't have anything to do with the caps? Most of the night looks/sounds fine, but the attached pic shows a stretch where the waveform is shifted up and clipping only on the top. WTF? Is that what phase shifting looks like? I was running XY indoors and had the caps were very much on top of each other, so I didn't think phase would be a problem. Or is this something else? At one point, I thought the caps might have been touching each other (no windscreens), but I wasn't sure. There is no obvious vibration sounds or anything like that, so I'm not sure they were touching at all. Could someone please explain what the hell happened because I'm confused? Operator error? New caps? Weird acoustics in the venue? Corrupt file?

Yup. The lopsided thing is the weird part. Can what you describe make it asymetrical?

CHURCH-AUDIO · « **Reply #16 on:** March 09, 2006, 11:27:52 PM »

Well in theory Yes because when you start playing around with a Non digital EQ you introduce phase shift it could also be a sound engineer reversing the polarity of the midrange or high end drives on a system. Most sound engineers have total control over a sound system and can play with shit like that. But that is a long shot I would try using the same gear with a home stereo and see what the wave forms look like see if you can get it to do the same wave form in a controlled space.

Quote from: Tainted on March 09, 2006, 11:20:57 PM

Quote from: CHURCH-AUDIO on March 09, 2006, 11:14:24 PM
This could be the front of house sound engineer bumping up a fader on his main system EQ. I do this from time to time to see if I have a bump in the front of house or if its comming off the stage monitor mix and when I hear something on the verge of feedback I will do it to see if its me or the monitor engineer. But still its strange its only on the + side of the wave form. Hummm maybe it could also be a sampling error?. Here is another theory What if the +- voltages on your computers PCI buss were out if you sound card is internal or even if you have a external with a voltage rail problem the opamps would have a swing towards the + or - depending on the design of the circuit.
Hey maybe its just a screwed up waveform? how does it sound?

Chris Church

Quote from: Tainted on March 09, 2006, 02:30:40 AM
Alright, maybe I'm just a newb, but I've got about 20 taping sessions under my belt at this point, and I have yet to come across this. It was my first night out with my new CK91 caps, but I'm guessing this didn't have anything to do with the caps? Most of the night looks/sounds fine, but the attached pic shows a stretch where the waveform is shifted up and clipping only on the top. WTF? Is that what phase shifting looks like? I was running XY indoors and had the caps were very much on top of each other, so I didn't think phase would be a problem. Or is this something else? At one point, I thought the caps might have been touching each other (no windscreens), but I wasn't sure. There is no obvious vibration sounds or anything like that, so I'm not sure they were touching at all. Could someone please explain what the hell happened because I'm confused? Operator error? New caps? Weird acoustics in the venue? Corrupt file?

Yup. The lopsided thing is the weird part. Can what you describe make it asymetrical?

BayTaynt3d · « **Reply #17 on:** March 10, 2006, 01:06:31 AM »

.

Alright, ALMOST ALL of the main act was fine. But on closer inspection, I found another short section that suffered the same fate. About 30 seconds worth. However, this sample might provide some insight possibly? The asymetry occurs exactly on time with the trombone (maybe it's the bass trombone) going for a really raspy lick. Maybe that mic was out of phase or something? Or maybe he was running through some sort of effects box? Could that cause this? You can download this 30 second MP3 and look at the waveform, it's not quite as pronounced as the waveform from the first act, but you can clearly see it, and you can clearly tell it occurs in sync with the trombone. This was the only 30 seconds out of more than two hours of the main act that I noticed anything. Maybe this had something to do with the venue? Or the PA? Or that trombone's phase or something? Is that possible?

-- DEAD LINK, SORRY --

.

BayTaynt3d · « **Reply #18 on:** March 10, 2006, 01:25:18 AM »

I should add that this was like a 15+ piece brass band, and this sample represents pretty much the only time that one trombonist soloed all by himself. So, it seems that out of two hours plus of music, it pops up only during his solo, which is kind of interesting. Maybe I'm reading too much into that, but maybe not?

CHURCH-AUDIO · « **Reply #19 on:** March 10, 2006, 01:58:49 AM »

I have heard the track and I think it has nothing to do with any sound engineer. It is from distortion I can hear it it's very hard to tell but I can hear it. I think it could be some strage power supply problem in a preamp or just plain old distortion it is electronic not accoustic. This type of distortion is called asymetrical hard clipping hard on the top of the wave form soft compression on the bottom. This from a preamp that ran out of gas what is your signal chain? exactly.

Quote from: Tainted on March 10, 2006, 01:25:18 AM

I should add that this was like a 15+ piece brass band, and this sample represents pretty much the only time that one trombonist soloed all by himself. So, it seems that out of two hours plus of music, it pops up only during his solo, which is kind of interesting. Maybe I'm reading too much into that, but maybe not?

SparkE! · « **Reply #20 on:** March 10, 2006, 10:50:03 AM »

Quote from: CHURCH-AUDIO on March 10, 2006, 01:58:49 AM

what is your signal chain? exactly.

Here's the signal chain from a previous post:

Quote from: Tainted on March 09, 2006, 10:58:16 PM

Chain was: CK391 > UA5 (BM2+) > JB3

It was the first night out with the 391's (I usually ran C4s). And I also think I used a spare DVD battery that I got with the FP24 I bought a few weeks back. So, I had some new things in the mix that possibly could had contributed maybe?

The good news is that the first and second sets of the main act look fine (see attachments). Not sure what happened on the opener though. Strange. I wonder if the caps ended up touched each other in my XY on the opener if that could have done it? I was running XY on stage, and although the opener wasn't miced through the PA, there was a crapload of mics and cables on stage for the main act that had 20+ artists in it, every one of whom was mic'ed. Not sure if I could have had problems with that. The main act, I pulled back to the sweet spot for the PA and went DINA, so I had a pretty different setup for the second part.

I'm still questioning whether there's an electrolytic cap in the signal chain that is getting back biased by the signal so that its impedance is a function of the instantaneous signal voltage. If that's the case, I'm suspecting that the problem is actually in the mics since he never had this problem before using these mics. When you get a new problem the first time you use new equipment, you've got to suspect the new equipment first, or at least suspect that it's a compatibility problem between the new equipment and your old equipment.

terrapinj · « **Reply #21 on:** March 10, 2006, 11:05:58 AM »

have you tried to duplicate the problem in front of your stereo?

SparkE! · « **Reply #22 on:** March 10, 2006, 11:28:38 AM »

Quote from: terrapinj on March 10, 2006, 11:05:58 AM

have you tried to duplicate the problem in front of your stereo?

This is the best question yet.

CHURCH-AUDIO · « **Reply #23 on:** March 10, 2006, 01:54:49 PM »

I looked at the wave form again but 100x magnification and it is harmonic distortion. Plain and simple Also I did suggest trying to use your home stereo and see if you could diplicate the problem but I highly doubt you would get the same SPL out of it.

Chris Church

Quote from: SparkE! on March 10, 2006, 10:50:03 AM

Quote from: CHURCH-AUDIO on March 10, 2006, 01:58:49 AM
what is your signal chain? exactly.

Here's the signal chain from a previous post:

Quote from: Tainted on March 09, 2006, 10:58:16 PM
Chain was: CK391 > UA5 (BM2+) > JB3

It was the first night out with the 391's (I usually ran C4s). And I also think I used a spare DVD battery that I got with the FP24 I bought a few weeks back. So, I had some new things in the mix that possibly could had contributed maybe?

The good news is that the first and second sets of the main act look fine (see attachments). Not sure what happened on the opener though. Strange. I wonder if the caps ended up touched each other in my XY on the opener if that could have done it? I was running XY on stage, and although the opener wasn't miced through the PA, there was a crapload of mics and cables on stage for the main act that had 20+ artists in it, every one of whom was mic'ed. Not sure if I could have had problems with that. The main act, I pulled back to the sweet spot for the PA and went DINA, so I had a pretty different setup for the second part.

I'm still questioning whether there's an electrolytic cap in the signal chain that is getting back biased by the signal so that its impedance is a function of the instantaneous signal voltage. If that's the case, I'm suspecting that the problem is actually in the mics since he never had this problem before using these mics. When you get a new problem the first time you use new equipment, you've got to suspect the new equipment first, or at least suspect that it's a compatibility problem between the new equipment and your old equipment.

BayTaynt3d · « **Reply #24 on:** March 10, 2006, 02:06:19 PM »

This weekend I'll record a test tone at home using both sets of mics and both caps on each mics (C4:card/omni & CK391/393) to see if I can recreate it. I'll also use my normal battery and the new (new to me, but old) battery I got with the FP24 I bought a while back. I'll do this all with the UA5 to see if I can force the issue. Any other things I should try?

BayTaynt3d · « **Reply #25 on:** March 10, 2006, 02:07:50 PM »

Also, so what is harmonic distortion? Is that gear related or FOH related or ?

CHURCH-AUDIO · « **Reply #26 on:** March 10, 2006, 03:02:20 PM »

If you look at the picture you will see your wave form and the wave form in the example are the same. I copyied this from this URL

http://en.wikipedia.org/wiki/Harmonic_distortion
there is some interesting info here hope this helps

Chris Church

Quote from: Tainted on March 10, 2006, 02:07:50 PM

Also, so what is harmonic distortion? Is that gear related or FOH related or ?

SparkE! · « **Reply #27 on:** March 10, 2006, 03:18:58 PM »

If your waveform is squashed on one side and expanded on the other (like yours was), that's a sign of even harmonic distortion. That distortion could have been actually present in the acoustic signal you recorded or it could have been induced by non-linearities in your recording signal path. If it was due to your own equipment, then when you play a pure tone through your speakers at HIGH levels and you record that sound, you will see not only the fundamental tone, but also mainly 2nd, 4th, 6th, 8th, ...., big even numberth harmonics. You might also see odd harmonics, but the even harmonics will be larger in general when asymmetric clipping or asymmetric expansion occurs. If you can't reproduce the problem when recording the sound from your home stereo (remember, it has to be LOUD!), then perhaps the problem was with the equipment at the venue where you recorded.

CHURCH-AUDIO · « **Reply #28 on:** March 10, 2006, 05:18:57 PM »

Thats true I have worked with alot of horn bands and heard this type of distortion. I think its caused by the horns them selves when air gets blown in it causes this very strange harmonic. Its almost like you can hear the spit inside the horn ( not joking ) Coltrain had that sound. Anyways Horn bands are a challange for any mic and preamp. When working with a all horn group or any horns play it safe on the gain give it lots of room. Thats what i do with a console channel its no different with a set of sensitive room mics also on the AKG mics your using make sure if they have a 10 db pad you use it for this type of work. Even tough there are guys out there that will say it will increase your noise floor. I would always use a pad on the mic when working with any type of horns and condenser mics.

Chris Church

Quote from: SparkE! on March 10, 2006, 03:18:58 PM

If your waveform is squashed on one side and expanded on the other (like yours was), that's a sign of even harmonic distortion. That distortion could have been actually present in the acoustic signal you recorded or it could have been induced by non-linearities in your recording signal path. If it was due to your own equipment, then when you play a pure tone through your speakers at HIGH levels and you record that sound, you will see not only the fundamental tone, but also mainly 2nd, 4th, 6th, 8th, ...., big even numberth harmonics. You might also see odd harmonics, but the even harmonics will be larger in general when asymmetric clipping or asymmetric expansion occurs. If you can't reproduce the problem when recording the sound from your home stereo (remember, it has to be LOUD!), then perhaps the problem was with the equipment at the venue where you recorded.

BayTaynt3d · « **Reply #29 on:** March 10, 2006, 05:27:45 PM »

Interesting stuff. I've just done a little reading, and I don't think I'm too worried about the harmonic distortion so much as what might be called, or at least looks like, DC OFFSET. Now maybe it is phase shifting or something else, and I plan on learning more this weekend, but I just found this interesting quote:

"Calling it "Centering" the wave is ambiguous -- perhaps this is something that Adobe should make note of. DC offset is easily diagnosed when there's a low-level signal, such as "open air," and the waveform sits off of the center line. Asymmetry is an entirely different matter, as you've all noted, and is usually caused by close-miking a voice, trumpet, trombone, or saxophone, all of which produce sounds with little puffs of air at the source. Andy & James, somewhere else it was noted that phase-shifting a voice could remove the asymmetry and allow a louder final result."

Now that's two "puffs" of air comments in a row, and all related to horns. Plus, it does look a little more "asymetrical" than strictly "off-center." Hmmm...

BayTaynt3d · « **Reply #30 on:** March 12, 2006, 12:11:06 AM »

Alright, I've had time for some tests at home. I, of course, could not achieve the same SPLs as the concert the other night, but this problem was entirely NOT reproduceable in a controlled environment. My test tone was centered perfectly around 0 (no DC offset at all) and the waveforms were perfectly symmetrical on the plus and minus side (no phase shift), and the waves were perfectly smooth (no harmonic distortion). Also, at this point, I've mastered the first opening set and both sets of the main act, and the only time this problem ever occured was when the TRUMPET (I said trombone before, but it was the trumpet) was "BLASTING." In fact, it was when the trumpet was soloing and blasting directly into the mic when this happened.

So, I'm pretty sure my gear is fine, which is kind of what I thought. And this exercise was useful for me because I learned a few things about phase shift, harmonic distortion, and DC offset. But, I'm still curious as hell at what exactly caused it? Was it the horn overloading/clipping the FOH's mic? Was the phase inverted on that mic/track at the FOH SBD somehow? Was the FOH's mic shot or defective? Or could this have been caused by a horn that is being "blasted"? Very interesting questions...

Thanks for all of your help, and I'll continue to watch this to see if it happens again, and whether it only happens with horns or only in that venue or whatever...

-- Taint

BayTaynt3d · « **Reply #31 on:** March 12, 2006, 01:04:07 AM »

Been on a little surfing rampage... And I'm beginning to think this has something to do with the natural harmonics and waveform shape that is associated with a brass instrument being BLASTED and MUTED at the same time (you know, a mute is that plunger they hold in front of the bell of the instrument). I'm not a 100% sure it was muted, but I think it might have been. And in a way, doesn't that make sense. Think about the polarity issues of making a matrix when you point your mics out at the audience and mix them in with the SBD with mics pointing back at the band. In that case, you're usually better off flipping the polarity. Well, when you mute a trumpet, aren't you forcing some of the sound back, around, and out of the bell (colliding with more sound coming out)? Alright, I'm probably making shit up at this point, but here's some more stuff I found...

Look at the example of a trumpet waveform discussed here:
http://www.st-and.demon.co.uk/AudioMisc/asymmetry/asym.html

Here's another quote:
"(a) audio signals are not always symmetric in electrical waveform (why should it always be? an oscillocope trace of a trumpet sound looks very asymmetrical & triangle in shape!)"

More:
http://www.klyne.com/pages/reviews4.html

As far as harmonic distortion is concerned, I think that might just be from the complexity of a brass instument maybe? See:
http://library.thinkquest.org/19537/Apps5.html

This quote was interesting from another site because it mentions "raspy," which is exactly what a trumpet sounds like when it is blasted, which is when I notice this the most:
"It can happen a lot with certain percussive instruments, it's very common on brass... Some vocalists - Especially the more "raspy" types. It can also be phase issues, could be compression settings... Not everything makes a perfectly balanced sine wave."

And although unrelated to my issue here, and although this seems obvious to me now, it's nonetheless a pretty interesting way to "hear" the seperation of your stereo image:

"To analyze music through A/B listening, connect the outputs of your source, such as a CD player, to two channels of a mixer. Pan both channels to the center, and then reverse the polarity on one of the channels. Any sounds that are equal in both channels of the mix are canceled out, because their polarities in one channel are inverted with respect to the same sounds in the other channel. The mono signal that remains contains the sounds that were panned to the left or right channel, but not both. (Sounds that are more pronounced in one channel than in the other in the stereo mix are reduced in volume in this inverted mono mix, but they are not eliminated completely.) Comparing this signal with the stereo mix, as well as with the complete (noninverted) mono signal, helps you learn more about the reverbs, backing parts, stereo spreads, and other details that are often masked by the more prominent parts of the mix."

Author Topic: What the? Strange Waveform? (Read 9063 times)

Roving Sign

Roving Sign

Roving Sign

CHURCH-AUDIO

CHURCH-AUDIO

CHURCH-AUDIO

CHURCH-AUDIO

CHURCH-AUDIO

CHURCH-AUDIO